1. Field of the Invention
The invention relates to a process of regenerating catalysts. In particular, it relates to the regenerating of platinum-containing zeolite catalysts which have been deactivated by coke build-up. Catalysts which may be regenerated by the process of the present invention include those that have become deactivated during hydrocarbon hydroprocesses, such as the reforming or catalytic dewaxing of hydrocarbon feedstocks.
2. Discussion of the Prior Art
Regeneration of platinum catalysts utilized in hydrocarbon hydroprocessing procedures such as reforming is known in the art. Processes which utilize chlorine and oxygen in catalyst reactivation are particularly well known. For example, U.S. Pat. No. 2,906,702 to Brennan et al discloses a method of restoring an alumina-supported platinum catalyst after deactivation occurring during the reforming of hydrocarbons. This method teaches contacting a deactivated platinum-alumina catalyst with a gaseous chlorine, fluorine, or other halogen or halogen-affording substance at an elevated temperature. U.S. Pat. No. 3,134,732 to Kearby et al teaches a method for reactivating noble metal catalyst supported on alumina by contacting the catalyst with halogen-containing gas, stripping excess halogen therefrom, and subjecting the resulting catalyst to a reduction step with a hydrogen-containing gas. In this disclosure, the agglomerated metal is present on the surface of the alumina as small crystallites. It is also known in the art to regenerate noble metal and platinum group metal-containing zeolite catalysts. Regeneration of noble metal-loaded zeolite catalysts required certain procedural modifications to regain the activity of the metal. U.S. Pat. No. 3,986,982 to Crowson et al treats deactivated platinum group metal-loaded zeolites by contacting them with a stream of an inert gas containing from 5 to 500 ppm volume of chlorine as chlorine, HCl, or an organic chlorine-containing material. The resulting catalyst is purged to remove residual oxygen and chlorine and then reduced in a stream of hydrogen at 200.degree. to 600.degree. C.
The treatment of noble metal-containing catalyst material with sulfur compounds is also known in the art. For example, U.S. Pat. No. 3,661,768 to Davis, Jr., et al describes a method of regenerating a bimetallic reforming catalyst, such as platinum-rhenium on alumina, which includes contacting the catalyst with hydrogen sulfide to convert platinum to platinum sulfide. Prior to sulfiding, the catalyst is contacted with chlorine and steam in order to effect chlorination.
Reactivating noble metal-containing catalyst material with water is also known in the art. For example, U.S. Pat. No. 4,480,144 to Smith discloses a regeneration process in which the catalyst is mildly steamed in order to enhance the catalyst activity. Specifically, the regeneration step comprises contacting the catalyst containing the carbonaceous materials with a continuous closed loop flow of a gas stream comprising oxidizing gas and steam at regeneration conditions. U.S. Pat. No. 3,899,411 to Hansford discloses a process directed to correcting "metal maldistribution". This rejuvenation process includes hydrating the catalyst in moist air, and then contacting the catalyst with gaseous ammonia until the liquid water phase is substantially saturated with ammonia. U.S. Pat. No. 3,855,343 to Huang et al discloses a regeneration process which utilizes a polar solvent, such as, e.g., water. U.S. Pat. No. 4,481,103 to Krambeck et al discloses an FCC cracking catalyst regeneration process in which the spent catalyst is contacted with steam at a temperature of 500.degree. to 700.degree. C. for about one to ten minutes. Additionally, a process for reactivating coked Y-type catalyst containing platinum or palladium hydrating the catalyst is disclosed in Rabo, Jule A., Ed. Zeolite Chemistry and Catalysis, American Chemical Society, Washington, D.C. (1968), pp. 576-578.
The regeneration of zeolite materials which contain noble metals, such as platinum, has been found to be particularly difficult. For example, some of the above treatments require certain precautions owing to the corrosive nature of the halogens used. Additionally, certain materials employed in these processes add significantly to the cost of catalyst regeneration. Further, in most of the above processes, catalysts in which the noble metal has been agglomerated thereon must be subsequently re-dispersed. For example, treatment of agglomerated platinum on silica, using a variety of chlorine-containing compounds with water and oxygen in an inert gas results in a large loss of platinum from the silica. Similarly, the zeolite regeneration process as described in U.S. Pat. No. 3,986,982 to Crowson et al has not been found suitable for use in regeneration of highly siliceous zeolites, i.e., zeolites having a framework silica-to-alumina ratio of at least about 20. Further, it has been found in commercial regeneration processes that the temperature parameters are difficult to control. In order to effectively regenerate a catalyst, the temperature must be high enough to keep the coke burning, but not so high as to agglomerate the metal on the catalyst. In commercial in situ units, if the oxygen begins to build up during the initial start-up phase due to the temperature falling below the ignition point, a subsequent rise in temperature will then have an uncontrolled burn effect on the zeolite catalyst, causing hot spots or flash burns. This uncontrolled temperature rise tends to facilitate noble metal agglomeration. Further, in a commercial reactor, the catalyst bed has to experience the burn for the entire reactor. In other words, the bottom of the catalyst bed experiences regeneration conditions at high temperatures for the entire regeneration process, which can be for a prolonged period.
It is thus an object to overcome the deficiencies of the prior art.
Further, it is an object to provide a process for regenerating a platinum-containing catalyst in which the platinum does not agglomerate on the catalyst.
Further still, it is an object of the present invention to provide a catalyst regeneration process which obviates the need to redisperse the platinum on the catalyst by regenerating the catalyst under controlled temperature and water conditions.